A multifunction printer has functions of a printer, a copy machine, a scanner, and the like. In recent years, such technologies are known that provides the multifunction printer with functions of displaying an operation screen for each user, limiting use of functions depending on a user, and performing the other operations. Such a multifunction printer carries out user authentication processing.
As a user authentication method adopted in a multifunction printer, the following two methods have been known conventionally: (a) a user inputs an ID (user identification information), and a password, and the ID and password are authenticated, (b) a user carries a memory card, and user identification information is read from the memory card via non-contact reading, and the user identification information is authenticated (see Patent Document 1 mentioned below).
The method (a), however, requires a user to input the ID and password via key operation, which is inconvenient to the user. On the other hand, the method (b) does not require such operation. However, with the method (b), it is necessary for a user to take measures not to lose, or not to forget to carry the memory card. Further, with either the method (a) or (b), impersonation is possible due to leakage or lending of the user identification information.
Furthermore, there is a possibility that a user's printed matter is accidentally taken by another user, when a plurality of users issues print instructions to a single multifunction printer. This causes trouble, especially in a case where the printed matter is a confidential document.    Japanese Unexamined Patent Publication No. 2005-244489 (Tokukai 2005-244489 (published on Sep. 8, 2005))